As is well known, the main advantage of a hydraulic mount is that damping can be obtained in warm weather as well as cold weather which is not possible with high damped rubber compounds such as butyl. In such hydraulic mounts, the damping is obtained by an elongated orifice which delays fluid transfer between two liquid filled chambers and wherein the peak damping frequency is determined by the length and diameter of the orifice. It is also known that the hydraulic damping can be controlled by the addition of a decoupler which allows for small mount displacements without significant liquid transfer through the orifice and thus without significant damping. This is desirable in isolating road induced vibrations from the vehicle body by providing for the engine to then operate as a dynamic damper to absorb these vibrations.
Previous decoupler designs generally relied on a direct sized opening through the decoupler which reduces the maximum damping available and causes the mount to have two damping ranges, i.e. a very low one below a certain small mount displacement and a very high one above this displacement. Typically, these prior decouplers consist of a solid, hard plastic diaphragm with leakage provided around the periphery or a flexible rubber diaphragm with either leakage around the periphery, or through a sized hole in the center of the diaphragm which seats against an opening in the partition supporting the decoupler so that there is still flow through the decoupler at large mount displacement to reduce the maximum damping. While these prior designs have proven generally satisfactory, further gains in vehicle ride are possible if the damping transition could be smoothened or feathered along with better control of the minimum and maximum damping.